The invention relates to devices suitable for use in a process for the separation of mixtures of liquids insoluble in each other, especially oil-like liquids and water, wherein the liquid mixture is brought into contact, under static liquid pressure without application of additional pressure, with one side of a sheet structure consisting of fibers or filaments permeable to only one of the liquids, whereby one of the liquids passes through the sheet structure, and the liquids are collected and/or drained off separately such as shown in copending application Ser. No. 870,257 filed Jan. 17, 1978.
According to said application, sheet structures of different materials such as fiber nonwovens, woven fabrics, knitted fabrics and even unsized papers can be used, provided they meet the requirement that they be permeable to only one of the liquids to be separated and furthermore that their strength and dimensional stability be sufficient for the intended end-uses. Suitable for this purpose are fiber nonwovens, for example, special paper machine nonwovens made of a mixture of 0-80 weight percent viscose fibers, 0-90 weight percent synthetic fibers, including at least 50 weight percent fibers with a high shrinkage capacity of at least 25%, 5-50 weight percent bonding fibers and 0-50 weight percent cellulose, which are consolidated by thermal treatment of the wet nonwoven, woven or knitted fabrics.
All known synthetic textile fibers, such as polyamides, polyesters, polyacrylonitrile, polyolefins, etc. can be used. Fibers obtained by spinning polymers at high draw-off speeds can be used as the high-shrinkage constituent, which may be composed of a copolyamide of 20% nylon salt and 8% caprolactam. Copolyamide fibers of 40% nylon salt and 60% caprolactam, which soften or melt in the presence of water at relatively low temperatures are suitable as bonding fibers.
Other essential features of the prior process are described in said copending application and are incorporated herein by reference.
As used herein, a sheet structure is considered permeable to a liquid, when such liquid, under operating conditions, i.e. under the static pressure exerted by such liquids on the sheet structure, passes through the sheet structure.
It is also possible to use sheet structures which when tested, as described in said application are permeable to both liquids but become impermeable to one liquid by being impregnated with the other liquid before use. In this case, the permeability measurement is performed with a previously soaked sheet structure. For instance, a sheet structure which in the "dry" stage is permeable both to water and oil can be first impregnated with water to make it impermeable to oil. For long-term use, it is, of course, necessary that the material never dry out.
To carry out the process of the copending application, it was found especially expedient to use a device comprising a tubular or pipe-shaped structure laid out across the direction of flow of the stream and provided over its entire length with a discontinuous slit, the width of the slit extending from above the liquid surface to below the contamination boundary. The slit was closed off by a sheet structure permeable to only one of the liquids to be separated and a collecting area is provided within the structure for the passing liquid.
The device may be anchored in the stream by means of floats, e.g. air hoses within the oil barrier, and moorings or the like.
The tubular, external covering of the device can be made of any suitable material impermeable to liquids, e.g. a plastic such as PVC or a plastic-laminated textile sheet structure. As material for the sheet structure which according to the invention is only permeable to e.g. the oil-like liquid to be separated but not to the other, e.g. water, use is preferably made of special paper machine nonwovens, as described in e.g. U.S. Pat. No. 3,394,047. Permeability or impermeability is determined under simulation of actual end-use conditions by DIN standards 53886. Such sheet structures are considered suitable for specific end-use purposes which under operational pressure conditions are permeable to one but not to the other liquid.
The version of the device illustrated in FIG. 3 of the copending application has been found eminently suitable whenever the flow rate of the open channel to be decontaminated was relatively slow and even. However, higher flow rates and/or irregular flow patterns lead to local compression or collapsing of the device.